1. Field of the Invention
The present invention relates to a laminated ceramic capacitor, and more particularly to a laminated ceramic capacitor, designed to realize a low equivalent series inductance (ESL) and a controllable equivalent series resistance (ESR) while realizing a high capacitance.
2. Description of the Related Art
A capacitor is a device for storing electricity, and is provided with two oppositely disposed electrode plates so that, when a voltage is applied to the capacitor, electric charges are accumulated in respective electrodes. When a direct voltage is applied to the capacitor, electric current flows in the capacitor during accumulation of the electric charges, whereas it does not flow in the capacitor after accumulation of the electric charges. When an alternating voltage is applied to the capacitor, the polarities of the electrodes are alternately varied, so that an alternating current continuously flows through the capacitor. Such a capacitor is generally indicated by an accumulative capacitance F.
Depending upon the dielectric material provided between the electrodes, capacitors can be classified into aluminum electrolysis capacitors which have aluminum electrodes and a thin oxide membrane between the aluminum electrodes, tantalum capacitors which are electrolysis capacitors having tantalum electrodes, ceramic capacitors which have a dielectric layer of a high dielectric constant, such as titanium-barium, provided between the electrodes, laminated ceramic capacitors which have multiple layers of ceramic material of a high dielectric constant as the dielectric material between the electrodes, and film capacitors which use polystyrene film as the dielectric material between the electrodes.
Among the above-mentioned capacitors, since the laminated ceramic capacitor has excellent temperature and frequency characteristics, and can be miniaturized, it has been applied to various electronic circuits.
FIG. 1 is a perspective view illustrating the outer appearance of a conventional laminated ceramic capacitor. Referring to FIG. 1, the conventional laminated ceramic capacitor 10 comprises a ceramic block 11, and external electrodes 12 and 13 formed on outer surfaces of the ceramic block 11 and set to positive and negative terminals, respectively.
The ceramic block 11 has two types of electrode patterns alternately arranged therein so as to be connected to positive and negative electrodes, respectively. Although the electrode patterns generally have a rectangular shape, the electrode patterns may have different shapes and arrangements in order to enhance characteristics of the capacitor.
FIG. 2 is an exploded perspective view illustrating the arrangement of internal electrodes of the conventional laminated ceramic capacitor. Referring to FIG. 2, the laminated ceramic capacitor has two types of rectangular internal electrode patterns 21 and 22 connected to different electrode terminals while being alternately laminated in the ceramic block. At this time, the internal electrode patterns 21 and 22 are provided with withdrawing patterns 21a and 22a connected to the external electrodes 12 and 13 formed on the outer surface of the ceramic block 11 such that voltages having opposite polarities can be applied to the internal electrode patterns 21 and 22, respectively.
In the laminated ceramic capacitor constructed as described above, when the voltages having the opposite polarities are applied to the internal electrode patterns 21 and 22 vertically adjacent to each other, electric charges are accumulated between the internal electrode patterns 21 and 22 having the opposite polarities, respectively. With such a construction, areas of the electrode patterns facing each other within the ceramic block are increased, so that the capacitor can have a high capacitance.
For such a laminated ceramic capacitor, a lower equivalent series inductance (ESL) is preferred. However, the equivalent series resistance (ESR) must be maintained above a certain level, and in some cases, it need to raise the ESR by user's request.
Meanwhile, in the case of the laminated ceramic capacitor as shown in FIG. 2, the positive and negative electrodes are alternately arranged, so that magnetic fluxes generated by high frequency currents flowing in the electrode patterns 21 and 22 facing each other are counterbalanced, thereby reducing ESL. However, not only is such reduction of the ESL insufficient to satisfy the requirements, but the ESR is also significantly lowered since resistances generated by the withdrawing patterns 21a and 22a formed to the internal electrode patterns 21 and 22, respectively, are connected in parallel.
The ESL is an unwanted component, which deteriorates the characteristics of the capacitors, and is increased in proportion to a path of electric currents flowing through the electrode patterns. Particularly, the ESL can be further increased if the electric currents flow in an identical direction through the electrode patterns 21 and 22 facing each other.
In order to reduce the ESL, the electric currents are changed to flow in different directions through adjacent internal electrode patterns 21 and 22, so that the magnetic fluxes generated by the electric currents are counterbalanced, thereby reducing the ESL. Alternatively, the path of the electric current is decreased, thereby reducing the ESL.
Referring to FIG. 2, the laminated ceramic capacitor are further provided with additional withdrawing patterns and formed in opposite directions, respectively, whereby the electric currents flowing in the internal electrode patterns 21 and 22 are guided to flow in opposite directions, thereby further reducing the ESL in comparison to the construction shown in FIG. 2.
However, with the constructions described above, the ESL cannot be completely prevented from being generated in the capacitor. In particular, in the case of decoupling capacitors applied to high frequency circuits, since a small ESL can influence the decoupling capacitors, it is necessary to further reduce the ESL, and the problem of generating a too low ESR is still present.
A laminated electronic component disclosed in Japanese Patent Laid-open Publication No. 2002-151349 has internal electrodes provided on a plurality of internal planes within a ceramic block while being formed as two ruler-shaped electrode patterns thereon. According to the disclosure, the two ruler-shaped electrode patterns are arranged in the same plane, such that electric currents can flow in opposite directions through the electrode patterns, thereby reducing ESL caused by high frequency current. A laminated electronic component disclosed in Japanese Patent Laid-open Publication No. 2002-164256 has internal electrodes provided on a plurality of internal planes within a ceramic block, in which each of the internal electrodes has a notch, and at least one pair of current paths are formed at both sides of the notch to allow the electric currents to flow in opposite directions through the current paths. According to this document, the electric currents flow in opposite directions through the two current paths within one internal electrode, thereby reducing ESL caused by high frequency current.
According to the above disclosures, although the ESL can be further reduced in comparison to the laminated devices shown in FIGS. 2 and 3, the reduced amount of the parasitic impedance does not satisfy the level required for the decoupling capacitors for high frequency circuits. Moreover, in the case of the high frequency circuit, since the ESL of the decoupling capacitors has a high influence on circuit capacitance, it is necessary to further reduce the ESL.
FIG. 3 is a laminated electronic capacitor disclosed in U.S. Pat. No. 6,441,459. Referring to FIG. 3, the laminated ceramic capacitor has internal electrodes 31–38, each having one withdrawing pattern 31a–38a, thereby satisfying the ESR. However, according to the disclosure, there is a problem in that the ESL is increased.